In the field of X-ray imaging, for example in computer tomography, angiography, or radiography, use can be made of counting direct-converting X-ray detectors or integrating indirect-converting X-ray detectors.
In direct-converting X-ray detectors, the X-ray radiation or the photons can be converted in to electrical pulses by a suitable converter material of the converter element. As direct-converting converter material, the following can be used for example: CdTe, CZT, CdZnTeSe, CdTeSe, CdMnTe, InP, TlBr2, HgI2, GaAs or others. The electrical pulses are evaluated by evaluation electronics, for example by an integrated circuit (Application Specific Integrated Circuit, ASIC).
In counting direct-converting X-ray detectors, incident X-ray radiation is measured by counting the electrical pulses which are triggered by the absorption of X-ray photons in the converter material. As a rule, the amount of the electrical pulse is proportional to the energy of the absorbed X-ray photon. This means that spectral information can be extracted by comparing the amount of the electrical pulse with a threshold value.
For the purpose of signal stabilization, the converter element, for example having CdZnTe, CdTe, CdHgTe, CMT, or the like, can be illuminated with additional electromagnetic radiation, for example visible light, IR or UV light. The illumination results in the formation of electron-hole pairs which flow away via the converter material and can contribute to an offset signal. By using the additional illumination, an improved short-term and long-term stability of the X-ray detector can be achieved.
Visible, infrared, ultraviolet, or long-wavelength light can pass through the converter material and emerge from the converter element on the side of the converter element facing away from the illumination source. The evaluation unit is generally located on the side facing away from the illumination source so that a light quantity of the additional illumination can penetrate the evaluation unit.
Optical photons can be absorbed in the converter element or can be reflected at the surface on the side of the converter element facing the illumination source so that they do not penetrate the converter element. Optical photons can be absorbed in an electrode on the side of the converter element facing away from the illumination source. Optical photons can penetrate directly, following scattering or reflection, in to the evaluation unit and interact with the evaluation unit. The evaluation unit can have amplifier structures with typically small capacitance which react very sensitively to the additional illumination. For example, electron-hole pairs can be generated directly in amplifying diode structures.
An X-ray detector is known from the as yet unpublished patent application 102015216527.2, the entire contents of which are incorporated herein by reference, which has a substrate with an electrically conducting connection between a readout contact in the region of the top side of the substrate and an input of a preamplifier in an active layer of an integrated circuit. A first electrically conducting connection is provided between the readout contact and a second electrically conducting connection. An area of a first light shield at the top side of the substrate is larger than an area of an optically transparent region in the substrate that is laterally delimited by a second light shield so that the area of the first light shield covers the area of the optically transparent region in a first projection along the surface normal. The second electrically conducting connection is provided inside a second projection of the area of the optically transparent region along the surface normal and below the second light shield. A third electrically conducting connection between the second electrically conducting connection and the preamplifier is provided below the second light shield.